The present invention relates to an optical fiber cable and optical fiber cable with plug used for optical signal transmission lines, computer connection lines for high-speed optical communications, lines around exchanges, lines for factory automated machinery control, data transmission lines for automobiles and other moving vehicles, and optical sensor lines.
The present application is based on a patent application filed in Japan (Japanese Patent Application No. Hei 11-37491 1), and the described contents of said Japanese application are partially incorporated in the present specification.
Plastic optical fibers (to be simply referred to as xe2x80x9coptical fibersxe2x80x9d) are already used practically in short-distance data communications and sensor applications. At such times, the optical fiber is infrequently used alone, but rather is frequently used in the form of an optical fiber cable in which the outside of the optical fiber is protected with a coating layer. In order to connect such optical fiber cables to a unit incorporated the light source and a sensor as signal sources, or to join the optical fiber cable to another optical fiber cable, the coating layer on the end of the cable is frequently peeled to expose the optical fiber and a plug component is attached to the end of the cable so that it is used in the form of an optical fiber cable with plug.
In such an optical fiber cable with plug, the coefficients of thermal expansion of each of the materials that compose the optical fiber, coating layer, and plug are different. In addition, the optical fiber is easy to contract due to relaxation of its orientation during spinning. Accordingly, phenomenon in which the end of the optical fiber protrudes or retracts from the end of the optical fiber cable with plug, namely the phenomenon of pistoning, may occur due to time-based changes or thermal hysteresis and the like of the optical fiber, coating and plug when the optical fiber cable is used. When this pistoning phenomenon occurs, the distance between the end of the optical fiber and the light source or light receiving element changes from its initial value resulting in a change in the amount of coupled light, which may cause problems.
On the other hand, such optical fiber cables are used vehicle mounting applications and in factory control equipment wiring applications. Since optical fiber cables used in such applications are exposed to environments in which lubricating oil, engine oil, and other organic solvents are used, they are required to have oil resistance. In order to impart oil resistance to optical fiber cables, a technology that uses an amide polymer for the coating layer is disclosed in Japanese Unexamined Patent Application, First Publication No. Sho 50-2552, Japanese Unexamined Patent Application, First Publication No. Hei 10-319281, and the like.
However, since these optical fiber cables do not have adequate flame resistance, there is the risk of these cables causing a fire to spread at the time of a fire. In addition, since the peel strength between the optical fiber and coating layer is low, pistoning phenomenon tended to occur easily in the case of using as an optical fiber cable with plug.
The object of the present invention is to provide an optical fiber cable having superior oil resistance and flame resistance, that is resistant to peeling of the optical fiber and coating layers, and to provide an optical fiber cable with plug that is resistant to the occurrence of pistoning phenomenon.
The optical fiber cable of the present invention is an optical fiber cable of diameter D1 (mm) in which an adhesive layer having a thickness of 0.5 to 200 xcexcm, a primary coating layer, and a secondary coating layer are sequentially formed around the outside of an optical fiber in which the outermost layer is composed of vinylidene fluoride polymer; wherein, in the case the diameter of the optical fiber is represented with Da (mm), the thickness of the adhesive layer is represented with d (mm), and Da+2d is represented with D2, then D1/D2=1.2 to 3.5. The optical fiber may be composed of a core, a sheath formed around the core, and a protective layer formed around the sheath.